Embodiments of the inventive concepts relate to image signal processing devices and methods. More particularly, embodiments of the inventive concepts related to a lens shading correction circuit, a system on chip including a lens shading correction circuit, a data processing system including a camera module and a lens shading correction circuit, and a data processing method for lens shading correction of an image.
The term “vignetting’ generally refers to a reduction in light intensity (or brightness) at the periphery of an image relative to the center of the image. Herein, the phrase “lens shading” refers to vignetting resulting from an amount of light reaching off-center positions of a sensor or film being less than the amount of light reaching the center of the sensor or film. The severity of vignetting is dependent upon, for example, the geometry of a lens positioned over the sensor or film, and can vary with focal length and f-stop setting. Generally, vignetting is more visually apparent in lenses of a lower f-stop (or larger aperture).
Lens shading correction techniques may be adopted in an attempt to compensate for adverse visual affects associated with vignetting. For example, to compensate for differing light intensities, components of a gain correction function used in image processing may be determined and set depending on a location within an image. In the case of a pixel image, for example, pixels located closer to a periphery of the image may be subject to greater gain than pixel nearer the center of the image. However, this can result in increased noise levels at the periphery, which can be particularly problematic at low luminance levels where noise is relatively high. This is because the lens shading compensation may entail applying different gains to different colors of an image signal, which may cause a noise power to be different among the colors. When the lens shading compensated signal is later applied to a low-pass filter to remove noise, the differing noise powers of the colors can create the appearance of a color (e.g., red, blue, or purple) distortion at the edge of the image.